Akihito Ozaki

Systematic analysis on combined heat and water transfer through porous materials based on thermodynamic energy

Abstract A new thermodynamic energy ‘water potential’ based on the principles of chemical potential of an element of mixed gas is defined as the driving force of gaseous phase water flux. Adhesive power or ‘capillary action’ and a portion of the water potential, is confirmed as the driving force of liquid phase water flux. A numerical model of combined heat and water transfer using the water potential is introduced and influences of forces, such as gravity and pressure on water flux are incorporated from the viewpoint of thermodynamics. A way to estimate diffusivities of gaseous and liquid phase water through porous materials is also shown. Accuracy of the numerical model is demonstrated through a comparison between calculation and experiment for different temperature gradients and water content in a porous material.

Study of Air-Conditioning Load: Comparison of Steel and RC Residence Units

Abstract Recently, the fight against global warming is becoming increasingly important. Being major energy consumers, air-conditioning (AC) loads are gaining importance. Therefore, the effects of heat insulation methods and AC usage patterns on AC loads should be verified before a building is constructed. This paper examines the AC loads of two typical residential units of steel (S) and reinforced concrete (RC). To compare and analyze these cases, THERB, software for dynamic simulation of the thermal environment of residential buildings, is employed to simulate the loads. Three common patterns based on the lifestyle in Japan are applied in this study to show that different family makeup can lead to varying AC loads. Further, two RC units (exterior wall insulated on the inside/outside) and one S unit (exterior wall insulated on the inside) are studied. The results reveal that the high heat capacity of concrete influences the living environment and causes differences between the RC and S units. The AC load of an RC unit with an exterior wall that is insulated on the inside is lower than that of a unit with an exterior wall that is insulated on the outside and is almost equal to that of the S unit.

Performance Evaluation of Residences by Dynamic Simulation: Heat Load Based on Changing the Location, Plan and Specification of Residences

Abstract The Japanese residential energy saving standard for new house generation was modified in 1999, in which ″specification standards″ were provided as decision criteria for designers. However, there are several methods for lowering the energy consumption of houses which are not evaluated by these standards. In this paper, we predict the change in heating and cooling load by difference of location, planning and specification of a model house, which are not evaluated by ″the specification standards″. We then examine the effectiveness of passive energy methods which are also not considered by the standard.

Systematic Analysis Model on Combined Heat and Water Transfer Using Water Potential Based on Thermodynamics

A thermodynamic energy “water potential” based on the principles of chemical potential of an element of mixed gas is defined as the driving force of gaseous phase water transfer. Adhesive power or “capillary action” and a portion of the water potential, is confirmed as the driving force of liquid phase water transfer. A numerical model of combined heat and water transfer using the water potential is introduced and influences of forces such as gravity and pressure on water transfer are incorporated from the viewpoint of thermodynamics. A way to estimate diffusivities of gaseous and liquid phase water through porous materials and the thermodynamic relations between such diffusivities and the potential are also shown. Accuracy of the numerical model is demonstrated through a comparison between calculation and experiment for different temperature gradients and water content in a porous material.